This invention relates to heat exchangers and, in particular to a heat exchanger assembly adapted for automotive or other air conditioning evaporators or condensers and which utilizes tubes of more than one diameter within the body of the heat exchanger heat transfer surface.
Where a heat exchanger utilizes a working fluid which exists in both the gaseous and liquid phase, heat transfer performance can be limited by excessive working fluid pressure drop in those areas where the gaseous phase working fluid is found. In a heat exchanger which operates as a condenser, this problem of pressure drop occurs in the inlet section; in a heat exchanger which operates as an evaporator, it is found in the outlet section.
In a condenser-type heat exchanger, pressure drop that occurs in the inlet section reduces the saturation temperature by an amount proportional to the pressure drop. This has the effect of reducing the temperature potential driving the exchange of heat from the internal fluid to the second working fluid (e.g., air) passing over the outside of the primary and secondary surfaces. In typical applications, these surfaces are the tubes and associated fins through which the working fluid passes. Efforts which have been employed to reduce pressure drop include multiple inlet feeds and manifold assemblies, which add cost and complexity and reduce the overall assembly reliability by virtue of increasing the number of variables in the production process.
In an evaporator-type heat exchanger, excessive pressure drops in the internal fluid path on the outlet side have a similar consequence, i.e., reduction in the temperature potential available to absorb heat from the air stream passing over the exterior of the heat exchanger tubes and fins.
Furthermore, use of heat exchangers in automotive (including truck and other motor vehicles) applications, such as air conditioning systems, requires that such units be compact, low in weight and highly efficient in order to meet the increasingly restrictive specifications in modern motor vehicle technology.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a heat exchanger assembly which minimizes the pressure drop associated with a dual phase working fluid in the gaseous phase.
It is another object of the present invention to provide a solution to the aforementioned problem of gaseous fluid pressure drop which can be utilized in both evaporators and condensers.
It is a further object of the present invention to provide a heat exchanger which meets the aforementioned objects and which is compact in configuration, low in weight and does not introduce unnecessary complexities in manufacturing.
It is yet another object of the present invention to provide a heat exchanger assembly which minimizes gaseous phase pressure drop of a dual phase working fluid which is especially suitable for use in automotive and other industrial, commercial or residential applications.
It is a further object of the present invention to provide a heat exchanger which may be utilized in various applications and which provides higher efficiencies over conventional industrial, commercial, residential or automotive type heat exchangers.